Sarcoidosis is a systemic granulomatous disease of unknown etiology that likely involves exposure to some environmental agent in a genetically susceptible host. We propose to identify sarcoidosis susceptibility genes and determine how these genes and environmental risk factors interact to cause sarcoidosis. This will be accomplished by organizing a ten center multicenter consortium to recruit an adequate sample of sarcoidosis families for analysis. We plan to use affected sibling pair linkage analysis to scan the genome for linked chromosomal regions, transmission disequilibrium testing to evaluate candidate genes in those regions with evidence for linkage and an environmental questionnaire to collect data to test for possible interactions of susceptibility genes with exogenous risk factors.